Communications method and apparatus

ABSTRACT

A communications method and apparatus are provided. The method includes: A first access network device sends a first message to a core network device, where the first message is used to indicate to suspend one or both of a first PDU session and a second PDU session. The first PDU session and the second PDU session are PDU sessions that are established as requested by a same terminal, and are used to transmit a duplicated data packet. According to the method, when a condition for implementing reliable transmission is not met, the core network device can be indicated to suspend the PDU session. In this way, a PDU session does not need to be re-established, and signaling overheads for establishing the PDU session are saved.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International Application No.PCT/CN2019/108722, filed on Sep. 27, 2019, which claims priority toChinese Patent Application No. 201811151716.6, filed on Sep. 29, 2018.The disclosures of the aforementioned applications are herebyincorporated by reference in their entireties.

TECHNICAL FIELD

Embodiments of this application relate to the field of communicationstechnologies, and in particular, to a communications method andapparatus.

BACKGROUND

With development of communications technologies, a duplicatetransmission scheme for data at a Packet Data Convergence Protocol(PDCP) layer is introduced. Generally, in a duplicate transmissionscheme, if a duplicate transmission function at the PDCP layer isconfigured and activated for a radio bearer (RB), an original datapacket generated at the PDCP layer is duplicated so that a same datapacket is obtained. The original data packet and the duplicated datapacket are then delivered by the PDCP layer to different radio linkcontrol (RLC) entities, and are transmitted to a Media Access Control(MAC) layer through different logical channels (LCH).

To ensure reliability of data transmission, the original data packet andthe duplicated data packet transmitted to the MAC layer are nottransmitted by using a same protocol data unit (PDU), becausetransmission of another PDU is not affected only if the original datapacket and the duplicated data packet are transmitted by using differentPDUs. Therefore, after two RLC entities transmit the two data packets todifferent MAC entities through different LCHs, two PDUs are formed fortransmission on different carriers.

To ensure end-to-end reliable transmission between a terminal and a corenetwork device, end-to-end redundancy transmission of data (for example,from the terminal to the core network device) is further introduced in5th Generation (5G) New Radio (NR) based on the foregoing scheme. Usingan example in which the redundancy transmission of data occurs from theterminal to the core network device in a dual connectivity (DC)scenario, the two PDUs formed at the terminal are sent to the corenetwork device by using different base stations. The two base stationsare respectively referred to as a master base station and a secondarybase station below.

Currently, in the DC scenario, before the terminal performs theredundancy transmission of data with the core network device by usingthe two different base stations, a PDU session needs to be establishedby the terminal, the master base station, and the core network device,and another PDU session needs to be established by the terminal, thesecondary base station, and the core network device. Therefore, theoriginal data packet and the duplicated data packet are transmitted byusing the two PDU sessions respectively. However, in the conventionaltechnology, there may be a case in which a terminal is unable to connectto the two base stations, and further research is required about how tohandle this case.

SUMMARY

Embodiments of this application provide a communications method andapparatus to optimize a processing process of a base station alreadyconnected to a terminal and of a core network device when the terminalis unable to connect to two base stations in a DC scenario.

According to a first aspect, an embodiment of this application providesa communication method. The method may be performed by a first accessnetwork device or a communications apparatus (for example, a chipsystem) that supports the first access network device in implementingthe method. This application is described by using an example in whichthe first access network device performs the method. In the method, thefirst access network device sends a first message to the core networkdevice. The first message is used to indicate to suspend one or both ofa first PDU session and a second PDU session. The first PDU session andthe second PDU session are PDU sessions that are established asrequested by a same terminal. The first PDU session and the second PDUsession are used to transmit a duplicated data packet. The first accessnetwork device may further send activation information to the corenetwork device. The activation information is used to activate thesuspended PDU session.

According to a second aspect, an embodiment of this application providesa communication method. The method may be performed by a core networkdevice or a communications apparatus (for example, a chip system) thatsupports the core network device in implementing the method. Thisapplication is described by using an example in which the core networkdevice performs the method. In the method, the core network devicereceives a first message from a first access network device. The firstmessage is used to indicate to suspend one or both of a first PDUsession and a second PDU session. The first PDU session and the secondPDU session are PDU sessions that are established as requested by a sameterminal. The first PDU session and the second PDU session are used totransmit a duplicated data packet. The core network device suspends oneor both of the first PDU session and the second PDU session based on thereceived first message.

According to a third aspect, this application provides a communicationsapparatus, including units or means (means) configured to perform thesteps in the first aspect or the second aspect.

According to a fourth aspect, this application provides a communicationsapparatus, including at least one processor and a memory. The at leastone processor is configured to perform the method provided in the firstaspect or the second aspect.

According to a fifth aspect, this application provides a communicationsapparatus, including at least one processor and an interface circuit.The at least one processor is configured to perform the method providedin the first aspect or the second aspect.

According to a sixth aspect, this application provides a communicationprogram. When the program is executed by a processor, the processor isconfigured to perform the method in the first aspect or the secondaspect.

According to a seventh aspect, a program product is provided, forexample, a computer-readable storage medium, including the program inthe sixth aspect.

It can be learned that, in the foregoing aspects, the first accessnetwork device can indicate, when a condition for implementing reliabletransmission is not met (for example, the terminal that requests toestablish the first PDU session and the second PDU session is unable toconnect to another access network device other than the first accessnetwork device), the core network device to suspend the PDU session.When the condition for implementing reliable transmission issubsequently met, the core network device may be indicated to activatethe suspended PDU session. In this way, a PDU session does not need tobe re-established, and signaling overheads for establishing the PDUsession are saved.

In a possible design, after receiving the activation information fromthe first access network device, the core network device may activatethe suspended PDU session based on the activation information. Accordingto this method, a PDU session does not need to be re-established, andthe signaling overheads for establishing the PDU session are saved.

In a possible design, before receiving the first message from the firstaccess network device, the core network device may further receive afirst session establishment request message from the terminal. The firstsession establishment request message includes a first identifier usedto identify the first PDU session. The first session establishmentrequest message is used to request to establish the first PDU session.The core network device determines, based on the first sessionestablishment request message, to establish the first PDU session. Inaddition, the core network device may further receive, from theterminal, a second identifier used to identify the second PDU session,and determine, based on the second identifier, to establish the secondPDU session. After determining to establish the first PDU session andthe second PDU session, the core network device may further send asecond message to the first access network device. The second messageincludes the first identifier and the second identifier. The secondmessage is used to request to establish the first PDU session and thesecond PDU session. Before sending the first message to the core networkdevice, the first access network device receives the second message fromthe core network device.

A message carrying the second identifier and sent to the core networkdevice is not limited in this application. In a possible design, thefirst session establishment request message further includes the secondidentifier. In another possible design, the second identifier is carriedin a second session establishment request message. The second sessionestablishment request message is used to request to establish the secondPDU session.

In a possible design, the second message further includes an associationindication. The association indication is used to indicate that thefirst PDU session is associated with the second PDU session.

In a possible design, after receiving the second message, the firstaccess network device determines, based on the second message, toestablish the first PDU session at the first access network device, andestablishes the second PDU session at the second access network device.In this design, when determining that there is no second access networkdevice that can establish the second PDU session, the first accessnetwork device sends the first message to the core network device.

In a possible design, when determining that there is a second accessnetwork device that can establish the second PDU session, the firstaccess network device sends the activation information to the corenetwork device.

In a possible design, the first access network device may further senddeactivation information to the core network device. The deactivationinformation is used to indicate to deactivate one or both of the firstPDU session and the second PDU session.

In a possible design, after receiving the deactivation information fromthe first access network device, the core network device may furtherdeactivate one or both of the first PDU session and the second PDUsession based on the deactivation information.

In a possible design, the deactivation information includes anidentifier of a to-be-deactivated PDU session.

In a possible design, the deactivation information includes anindication information element. The indication information element isused to indicate to deactivate one or both of the first PDU session andthe second PDU session.

In a possible design, the first message includes a first informationelement and/or a second information element. The first informationelement is used to indicate to suspend the first PDU session and/or thesecond PDU session. The second information element is used to indicate asuspension cause.

In a possible design, the activation information includes an identifierof a to-be-activated PDU session.

In a possible design, the activation information includes an indicationinformation element. The indication information element is used toindicate to activate one or both of the first PDU session and the secondPDU session.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic flowchart of implementing a duplicate transmissionfunction at a PDCP layer by a terminal;

FIG. 2 is a schematic diagram of a network architecture according to anembodiment of this application;

FIG. 3 is a schematic diagram of another network architecture accordingto an embodiment of this application;

FIG. 4 is a schematic diagram of a communications system according to anembodiment of this application;

FIG. 5 is a schematic flowchart of a communication method according toan embodiment of this application;

FIG. 6A and FIG. 6B are a schematic flowchart of another communicationmethod according to an embodiment of this application;

FIG. 7A and FIG. 7B are a schematic flowchart of still anothercommunication method according to an embodiment of this application;

FIG. 8A and FIG. 8B are a schematic flowchart of still anothercommunication method according to an embodiment of this application;

FIG. 9 is a schematic structural diagram of a communications apparatusaccording to an embodiment of this application;

FIG. 10 is a schematic structural diagram of another communicationsapparatus according to an embodiment of this application;

FIG. 11 is a schematic structural diagram of another communicationsapparatus according to an embodiment of this application; and

FIG. 12 is a schematic structural diagram of another communicationsapparatus according to an embodiment of this application.

DESCRIPTION OF EMBODIMENTS

To make the objectives, technical solutions and advantages of theembodiments of this application clearer, the following further describesthe embodiments of this application in detail with reference to theaccompanying drawings.

In the following, some terms of the embodiments of this application aredescribed, so as to help a person skilled in the art have a betterunderstanding.

(1) A terminal: a terminal includes a device that provides a user withvoice and/or data connectivity, for example, may include a handhelddevice with a wireless connection function, or a processing deviceconnected to a wireless modem. The terminal may communicate with a corenetwork by using a radio access network (RAN), and exchange voice and/ordata with the RAN. The terminal may include user equipment (UE), awireless terminal, a mobile terminal, a subscriber unit (subscriberunit), a subscriber station (subscriber station), a mobile station(mobile station), a mobile console (mobile), a remote station (remotestation), an access point (AP), a remote terminal (remote terminal), anaccess terminal (access terminal), a user terminal (user terminal), auser agent (user agent), a user device (user device), or the like. Forexample, the terminal may include a mobile phone (or referred to as a“cellular” phone), a computer with a mobile terminal, a portable,pocket-sized, handheld, in-computer or in-vehicle mobile apparatus, or asmart wearable device. For example, it may include a device such as apersonal communication service (PCS) phone, a cordless telephone set, asession initiation protocol (SIP) phone, a wireless local loop (WLL)station, or a personal digital assistant (PDA). The terminal furtherincludes a limited device, such as a device with a lower powerconsumption, or a device with a limited storage capacity, or a devicewith a limited computing capability. For example, the terminal includesinformation sensing devices such as a barcode identification device, aradio frequency identification (RFID) device, a sensor, a GlobalPositioning System (GPS), or a laser scanner.

As an example instead of a limitation, in this embodiment of thisapplication, the terminal may alternatively be a wearable device. Thewearable device may also be referred to as a wearable smart device, andis a collective term for wearable devices developed by intelligentlydesigning everyday wearables based on a wearable technology, forexample, glasses, gloves, a watch, clothing, and shoes. The wearabledevice is a portable device that is directly worn on a human body orintegrated into a user's clothing or accessory. A wearable device ismore than a hardware device, and can even achieve powerful functionsthrough software support, data interaction, and cloud interaction. In abroad sense, wearable smart devices include functionally complete andlarge-sized devices capable of implementing complete or partialfunctions independently of a smartphone, for example, a smart watch orsmart glasses, and also include devices dedicated to a type ofapplication function and used with support of such other devices as asmartphone, for example, various smart bands, smart helmets, and smartjewelry for health monitoring.

(2) Network device: a network device may include an access network (AN)device or a core network (CN) device. The access network device may alsobe referred to as a base station, or an access point (AP), or may be adevice in communication with a wireless terminal device by using one ormore cells over an air interface in an access network. Currently, someexamples of the access network device are: a next-generation NodeB(gNB), a transmission reception point (TRP), an evolved NodeB (eNB), aradio network controller (RNC), a NodeB (NB), a base station controller(BSC), a base transceiver station (BTS), a home base station (such as ahome evolved NodeB or a home NodeB, HNB), a baseband unit (BBU), awireless fidelity (WiFi) access point (AP), or the like. In a networkstructure, the network device may include a centralized unit (CU) node,a distributed unit (DU) node, or a RAN device including a CU node and aDU node. The core network device may be a mobility management entity(MME) in LTE, or may be a gateway (gateway), or may be a control plane(CP) network function (NF) or a user plane (UP) network function in a 5Gnetwork, for example, a common control plane network function (CCNF), asession management network function (SMF), an access and mobilitymanagement function (AMF), or the like.

Communication between the RAN device and the terminal complies with aprotocol layer structure. For example, a control plane protocol layerstructure may include functions of protocol layers such as a radioresource control (RRC) layer, a Packet Data Convergence Protocol (PDCP)layer, a radio link control (RLC) layer, a Media Access Control (MAC)layer, and a physical layer. A user plane protocol layer structure mayinclude the functions of the protocol layers such as the PDCP layer, theRLC layer, the MAC layer, and the physical layer. In an implementation,a Service Data Adaptation Protocol (SDAP) layer may be further includedat the PDCP layer.

The RAN device may use one node to implement the functions of theprotocol layers such as the radio resource control (RRC) layer, thePacket Data Convergence Protocol (PDCP) layer, the radio link control(RLC) layer, and the Media Access Control (MAC) layer; or, may use aplurality of nodes to implement the functions of the protocol layers.For example, in an evolved structure, the RAN device may include acentralized unit (CU) and a distributed unit (DU). A plurality of DUsmay be centrally controlled by one CU. The CU and the DU may beallocated based at the protocol layers of a wireless network. Forexample, the functions of the PDCP layer and the protocol layers abovethe PDCP layer are allocated to the CU, and the functions of theprotocol layers below the PDCP layer such as the RLC layer and the MAClayer are allocated to the DU.

The allocation at such protocol layers is merely an example. Theallocation may also be performed at other protocol layers such as theRLC layer, so that the functions of the RLC layer and the protocollayers above the RLC layer are allocated to the CU and that thefunctions of the protocol layers below the RLC layer are allocated tothe DU. Alternatively, the allocation is performed within a protocollayer. For example, some functions of the RLC layer and the functions ofthe protocol layers above the RLC layer are allocated to the CU, andremaining functions of the RLC layer and the functions of the protocollayers below the RLC layer are allocated to the DU. In addition, theallocation may also be performed in another manner, for example, basedon a delay, so that a function whose processing time needs to meet adelay requirement is allocated to the DU, and a function whoseprocessing time does not need to meet the delay requirement is allocatedto the CU.

(3) Dual connectivity (DC): means that a terminal is connected to twobase stations concurrently. The two base stations connected to theterminal may be base stations in a same radio access technology. Forexample, both of the two base stations connected to the terminal arebase stations in an LTE system or base stations in an NR system.Alternatively, the two base stations connected to the terminal may bebase stations in different radio access technologies. For example, onebase station connected to the terminal is a base station in the LTEsystem, and the other base station connected to the terminal is a basestation in an NR system. In this case, the DC is also referred to asmulti-radio access technology DC (multi-rat DC). For ease ofdescription, the DCs in different cases are hereinafter collectivelyreferred to as DC.

(4) Carrier aggregation (CA): a CA technology is used to aggregate aplurality of component carriers (CC) to serve one terminal to achieve awider transmission bandwidth and effectively increase uplink anddownlink transmission speeds.

(5) The terms “system” and “network” may be used interchangeably in theembodiments of this application. “A plurality of” means two or more.Therefore, in the embodiments of this application, “a plurality of” mayalso be understood as “at least two”, and “at least two” means two ormore. “At least one” may be understood as one or more, for example, one,two, or more. For example, “including at least one” means that one, two,or more are included, without limiting which items are included. Forexample, if at least one of A, B, or C is included, the included itemsmay be A alone, B alone, C alone, both A and B, both A and C, both B andC, or, all of A, B, and C. Similarly, the phrases such as “at least onetype” are also understood in a similar way. The term “and/or” describesan association relationship for describing associated objects andrepresents that three relationships may exist. For example, A and/or Bmay represent the following three cases: Only A exists, both A and Bexist, or only B exists. In addition, the character “/” usuallyindicates an “or” relationship between the associated objects unlessotherwise specified.

In addition, unless otherwise specified to the contrary, ordinal wordssuch as “first” and “second” mentioned in the embodiments of thisapplication are used to distinguish between a plurality of objects, butare not used to limit a sequence, a time sequence, a priority, or animportance degree of the plurality of objects. For example, the firstPDU session and the second PDU session are merely used to distinguishbetween different PDU sessions, but do not indicate that priorities,importance, or the like of the two PDU sessions are different.

The foregoing describes some concepts related to the embodiments of thisapplication. The following describes technical features related to theembodiments of this application.

In the 5G NR system, to ensure a low latency and high reliability ofservices such as ultra-reliable and low-latency communication (URLLC), aduplicate (duplication) transmission scheme for data at the PDCP layeris introduced.

The following describes how the duplicate transmission function at thePDCP layer is implemented at a terminal side.

Refer to FIG. 1, which shows a process by which a terminal implementsthe duplicate transmission function at a PDCP layer. Assuming that theduplicate transmission function at the PDCP layer is configured andactivated for a radio bearer (RB), each original data packet generatedat the PDCP layer, such as a PDCP protocol data unit (PDU), isduplicated, and then the original data packet and the duplicated datapacket are delivered by the PDCP layer to different RLC entities such asRLC 1 and RLC 2 in FIG. 1, and are transmitted to the MAC layer throughdifferent LCHs. In the example described here, the data packets aredelivered to two RLC entities. Alternatively, a data packet may beduplicated into a plurality of counterparts and transmitted by more thantwo RLC entities. To ensure reliability of data transmission, theoriginal data packet and the duplicated data packet transmitted to theMAC layer may be transmitted by using different carriers/cells, so as toensure that the original data packet and the duplicated data packet aretransmitted through two independent transmission paths. Because the datapackets are transmitted through different transmission paths, loss ofthe data packet transmitted on one transmission link does not affecttransmission of the data packet transmitted on the other transmissionlink, thereby doubling the reliability. Therefore, after the RLC 1 andthe RLC 2 in the terminal transmit the two data packets to the MACentity through different LCHs, the two data packets are respectivelytransmitted on different carriers/cells. As shown in FIG. 1, two PDUsare formed and then sent on a carrier 1 and a carrier 2 respectively.

The following uses two RLC entities and a DC scenario as an example todescribe how to implement a transmission function at the PDCP layer.

Refer to FIG. 2, which shows a network architecture by which theduplicate transmission function is implemented at the PDCP layer in theDC scenario. With respect to a base station, the DC scenario relates toa master base station and a secondary base station. Networkarchitectures of the master base station and the secondary base stationwith respect to one radio bearer are shown in FIG. 2. A networkarchitecture of a terminal with respect to the radio bearer includes thenetwork architecture of the master base station and the networkarchitecture of the secondary base station shown in FIG. 2. In otherwords, with respect to the radio bearer, the terminal includes one PDCPentity, two RLC entities, and two MAC entities. The PDCP entity, thePDCP layer, and the PDCP may be understood as a same concept. Similarly,the RLC entity, the RLC layer, and the RLC may be understood as a sameconcept, and the MAC entity, the MAC layer, and the MAC may beunderstood as a same concept. In the DC scenario, one terminal isconnected to two base stations concurrently, that is, a master basestation and a secondary base station. If the duplicate transmissionfunction at the PDCP layer is configured for a radio bearer, two datapackets duplicated at the PDCP layer are transmitted to two differentRLC entities, and are transmitted to the MAC entities through differentlogical channels. Finally, the two data packets are transmitted ondifferent carriers. This process is the same for both the base stationand the terminal. A difference is that, for the base station, the PDCPlayer in the master base station transmits the original data packet andthe duplicated data packet to different RLC entities respectively. Thetwo RLC entities are respectively located in the master base station andthe secondary base station. Subsequently, the RCL entity in the masterbase station transmits the received data packet to the MAC entity in themaster base station, and the RCL entity in the secondary base stationtransmits the received data packet to the MAC entity in the secondarybase station. The two MAC entities transmit the data packets by usingtheir respective carriers. For the terminal, the process is the sameexcept that the two RCL entities and the two MAC entities are located inthe terminal.

In a 5G NR system, to ensure end-to-end reliable transmission betweenthe terminal and a core network device, end-to-end reliable transmission(also referred to as end-to-end redundancy transmission of data) betweenthe terminal and the core network device is further introduced based onthe foregoing scheme.

The following describes duplicate transmission between the terminal andthe core network device by using two RLC entities and a DC scenario asan example.

Refer to FIG. 3, which shows a network architecture by which end-to-endreliable transmission is implemented between the terminal and the corenetwork device in a DC scenario. In the DC scenario, using uplink datatransmission as an example, the terminal may form two same data packets.In a possible implementation, the terminal generates a duplicated(duplication) data packet by using an existing protocol such as a FrameReplication and Elimination for Reliability (frame replication andelimination for reliability) protocol. In another possibleimplementation, the terminal may generate two same PDCP PDUs at anaccess layer such as a PDCP layer. In this application, the same datapacket may be referred to as a duplicated (duplication) data packet.This application does not limit how the terminal generates theduplicated data packet. After forming the two duplicated data packets,the terminal may send the two duplicated data packets to the corenetwork device by using a master base station and a secondary basestation respectively. Before sending the duplicated data packets to thecore network device by using the master base station and the secondarybase station, the terminal establishes a PDU session such as a PDUsession 1 in FIG. 3 by using the terminal, the master base station, andthe core network device, and establishes another PDU session such as aPDU session 2 in FIG. 3 by using the terminal, the secondary basestation, and the core network device. Further, the duplicated datapackets are transmitted through the two PDU sessions. In this way, theterminal can send the same data packet to the core network device twice,thereby improving data transmission reliability.

As can be learned from the foregoing description, the terminal isconnected to two base stations to implement end-to-end reliabletransmission between the terminal and the core network device. However,due to mobility of the terminal and a time-varying characteristic of anair interface channel, the terminal may be unable to connect to two basestations in some scenarios. Therefore, further research is required todetermine how to implement end-to-end reliable transmission between theterminal and the core network device in a scenario in which the terminalis able to connect to just one base station and in which the corenetwork device has prepared resources for establishing two PDU sessionsfor the terminal to transmit the duplicated data packets.

In view of this, an embodiment of this application provides a technicalsolution. In the embodiment of this application, assuming that theterminal is connected to just one master base station, the terminal mayinitiate establishment of a PDU session with the core network device byusing the connected master base station. The core network device mayprepare, by using a PDU session establishment request sent by the masterbase station, a resource used to carry the PDU session. If the masterbase station determines that the terminal is currently unable toconcurrently connect to another secondary base station, the master basestation may send a first message to the core network device. The firstmessage is used to indicate to suspend the PDU session that the terminalrequests to establish, so that the core network device suspends, basedon the first message, the PDU session that the terminal requests toestablish. When the master base station subsequently determines that theterminal can be concurrently served by both the master base station andthe other secondary base station, the master base station sendsactivation information to the core network device. The activationinformation is used to activate the suspended PDU session, so that thecore network device activates the suspended PDU session based on theactivation information.

The technical solution provided in this embodiment of this applicationis applicable to a 5G NR system, or applicable to a next-generationmobile communications system or another similar communications system.This is not specifically limited. In addition, the technical solutionprovided in this embodiment of this application is applicable to a CAscenario, or applicable to a DC scenario, or applicable to anotherscenario.

Refer to FIG. 4, which is a schematic diagram of a communications systemto which an embodiment of this application is applicable. As shown inFIG. 4, a terminal accesses a wireless network to obtain a service froman external network (for example, the Internet) by using the wirelessnetwork, or to communicate with another terminal by using the wirelessnetwork. The wireless network includes two access network devices and acore network device. The two access network devices are a first accessnetwork device and a second access network device. A scenario shown inFIG. 4 may be understood as a DC scenario. The terminal may beconcurrently connected to both the first access network device and thesecond access network device, and the terminal can communicate with bothof the two access network devices. The first access network device andthe second access network device are configured to connect the terminalto the wireless network. The first access network device may be a masteraccess network device of the terminal, and the second access networkdevice may be a secondary access network device of the terminal.Alternatively, the first access network device is a secondary accessnetwork device of the terminal, and the second access network device isa master access network device of the terminal. For example, both accessnetwork devices are base stations. In this case, the master accessnetwork device is a master base station, and the secondary accessnetwork device is a secondary base station. The first access networkdevice may work in an Evolved Universal Mobile Telecommunications SystemTerrestrial Radio Access (E-UTRA) system, the second access networkdevice may work in an NR system. Alternatively, the first access networkdevice may work in an NR system, and the second access network devicemay work in an E-UTRA system. Alternatively, for example, both the firstaccess network device and the second access network device work in an NRsystem, or in an E-UTRA system. The core network device is configured tomanage the terminal and provide a gateway for communication with theexternal network.

For example, the access network devices (the first access network deviceand the second access network device) in FIG. 4 are base stations. Indifferent systems, the access network devices correspond to differentdevices. For example, in a fourth generation mobile communicationstechnology (4G) system, an access network device may correspond to aneNB. For another example, in a fifth generation mobile communicationstechnology (5G) system, an access network device may correspond to agNB.

With reference to accompanying drawings, the following describes thetechnical solutions provided in the embodiments of this application.

Refer to FIG. 5, which shows a communication method according to anembodiment of this application. The method is applicable to the scenarioshown in FIG. 4. If the method is applied to the scenario shown in FIG.4, a first access network device referred to in the method may be afirst access network device in the scenario shown in FIG. 4, a secondaccess network device referred to in the method may be a second accessnetwork device in the scenario shown in FIG. 4, and a core networkdevice referred to in the method may be a core network device in thescenario shown in FIG. 4. For example, the first access network deviceand the second access network device may be base stations, and the corenetwork device may be an MME, an AMF, an SMF, or the like.

Referring to FIG. 5, the communication method may include the followingprocessing process.

S101: The first access network device sends a first message to the corenetwork device. The first message may be used to indicate to suspend oneor both of a first PDU session and a second PDU session, or, asunderstood in a different way, to suspend the first PDU session and/orthe second PDU session. The first PDU session and the second PDU sessionmay be PDU sessions that a same terminal requests to establish. Thefirst PDU session and the second PDU session are used to transmit aduplicated data packet. The first PDU session and the second PDU sessionmay be understood as PDU sessions that are a duplicate or redundancy ofeach other. For ease of description in this application, the PDUsessions that are a duplicate or redundancy of each other arecollectively referred to as duplicated PDU sessions.

Establishment of the first PDU session and the second PDU session may beproactively initiated by a same terminal, or may be passively initiatedby a same terminal. When the same terminal passively initiatesestablishment of the first PDU session and the second PDU session,before initiating establishment of the PDU session, the terminal mayreceive a trigger message sent by a network device. The trigger messagemay include an application indication. The application indication isused to indicate, to the network device, an application that expects theterminal to send a PDU session establishment request. The terminal maytrigger a PDU session establishment process based on the triggermessage.

In this embodiment of this application, the terminal initiatingestablishment of the first PDU session and the second PDU session may bea terminal accessing the first access network device, or may beunderstood as a terminal served by the first access network device.Unless otherwise specified, a terminal hereinafter referred to in thisapplication means such a terminal.

In this embodiment of this application, the duplicated data packet maybe a data packet that carries same content. Using uplink transmission asan example in which a terminal sends a data packet to a network device(such as a core network device or a gateway), assuming that the datapacket that the terminal needs to send to the network device is a firstdata packet, the terminal duplicates the first data packet to obtain asecond data packet that is the same as the first data packet, and thensends the first data packet and the second data packet to the networkdevice. In this application, the first data packet and the second datapacket are collectively referred to as duplicated data packets.Correspondingly, downlink transmission is similar to uplink transmissionexcept that the duplicated data packets are generated at the networkdevice. A quantity of first data packets is not limited in thisembodiment of this application. There may be one or more first datapackets. Understandably, because the second data packet is a data packetobtained by duplicating the first data packet, when the quantity of thefirst data packet is one, a corresponding quantity of the second datapacket is also one; and, when the quantity of the first data packets isplural, a corresponding quantity of the second data packets is alsoplural.

Using a DC scenario as an example, the first PDU session in thisapplication may be a PDU session that the terminal requests to establishwith the core network device by using the first access network device.For example, the first PDU session may be a PDU session 1 in FIG. 3. Inthis case, the first access network device may be a master base stationin FIG. 3. The second PDU session may be a PDU session that the terminalrequests to establish with the core network device by using anotheraccess network device different from the first access network device.For example, the second PDU session may be a PDU session 2 in FIG. 3. Inthis case, the other access network device may be a secondary basestation in FIG. 3. This application is described by using an example inwhich the first PDU session is a PDU session that the terminal requeststo establish with the core network device by using the first accessnetwork device, and in which the second PDU session is a PDU sessionthat the terminal requests to establish with the core network device byusing another access network device.

In this embodiment of this application, the first message may be a PDUsession resource establishment response (PDU session resource setupresponse) message, or a dedicated message used to suspend a PDU session.For example, the dedicated message may be a PDU session suspensionmessage.

Optionally, the first message may carry an identifier of the first PDUsession and/or an identifier of the second PDU session. For example, ifthe first message is used to indicate to suspend the first PDU sessionand the second PDU session, the first message may carry the identifierof the first PDU session and the identifier of the second PDU session.For another example, if the first message is used to indicate to suspendthe first PDU session, the first message may carry the identifier of thefirst PDU session. For another example, if the first message is used toindicate to suspend the second PDU session, the first message may carrythe identifier of the second PDU session.

The identifier of the first PDU session is used to uniquely identify thefirst PDU session, and the identifier of the second PDU session is usedto uniquely identify the second PDU session. In this embodiment of thisapplication, for ease of description, the identifier of the first PDUsession is referred to as a first identifier, and the identifier of thesecond PDU session is referred to as a second identifier.

Optionally, the first message may explicitly or implicitly indicate tosuspend the first PDU session and/or the second PDU session. When thefirst message explicitly indicates to suspend the first PDU sessionand/or the second PDU session, the first message may carry a firstinformation element (also referred to as indication information). Thefirst information element is used to indicate the core network device tosuspend the first PDU session and/or the second PDU session.Implementations of explicit and implicit indication are described indetail below, details of which are omitted here.

Optionally, the first access network device may further add a secondinformation element to the first message. The second information elementmay be used to indicate a suspension cause. An example of the suspensioncause is: the first access network device is unable to prepare for DCestablishment for the terminal initiating establishment of the first PDUsession and the second PDU session. Another example of the suspensioncause is resource shortage whereby the first access network device orthe second access network device is unable to provide a resourcerequired for establishing the first PDU session or the second PDUsession.

In a possible implementation, the first message may be further used toindicate to temporarily reject the first PDU session and/or the secondPDU session. Alternatively, as understood in a different way, the firstmessage is used to notify the core network device that a resource usedto carry the first PDU session and/or the second PDU session temporarilydoes not need to be released. Alternatively, as understood in adifferent way, the first message is used to notify the core networkdevice that the first PDU session and/or the second PDU sessiontemporarily do not need to be released. The resource used to carry thefirst PDU session and/or the second PDU session may be, for example, acore network tunnel (tunnel) used to carry the first PDU session and/orthe second PDU session and a reserved resource. In this example, afterreceiving the first message, the core network device may temporarilyretain, for future use, the established core network tunnel (tunnel)used to carry the first PDU session and/or the second PDU session andthe reserved resource. In this implementation, the first message may bea PDU session resource establishment response (PDU session resourcesetup response) message, or may be a dedicated message used to indicateto temporarily reject establishment of the first PDU session and/or thesecond PDU session. For example, the dedicated message may be a PDUsession rejection message. In this implementation, the first informationelement may be used to indicate to temporarily reject the first PDUsession and/or the second PDU session. The second information elementmay be used to indicate a rejection cause. The rejection cause mayinclude a cause for temporary inability to establish the first PDUsession and/or the second PDU session. For example, the first accessnetwork device is unable to prepare for DC establishment for theterminal initiating establishment of the first PDU session and thesecond PDU session. For another example, the rejection cause may furtherinclude resource shortage whereby the first access network device or thesecond access network device is unable to provide a resource requiredfor establishing the first PDU session or the second PDU session.

Optionally, in the foregoing possible implementation, the first messagemay carry a first identifier and/or a second identifier. For example, ifthe first message is used to indicate to temporarily reject the firstPDU session and the second PDU session, the first message may carry thefirst identifier and the second identifier. For another example, if thefirst message is used to indicate to temporarily reject the first PDUsession, the first message may carry the first identifier. For anotherexample, if the first message is used to indicate to temporarily rejectthe second PDU session, the first message may carry the secondidentifier.

In this application, temporary rejection may be understood as rejectionwithin a preset time. The preset time may be understood as a time from afirst moment to a second moment. The first moment may be a moment atwhich the first access network device sends the first message to thecore network device, and the second moment may be a moment at which thefirst access network device sends the activation information to the corenetwork device (S103).

Step S101 in this embodiment of this application may be understood ascorresponding to the following three solutions.

First solution: The first access network device sends the first messageto the core network device, where the first message is used to indicateto suspend the first PDU session and the second PDU session.

Second solution: The first access network device sends the first messageto the core network device, where the first message is used to indicateto suspend the first PDU session.

Third solution: The first access network device sends the first messageto the core network device, where the first message is used to indicateto suspend the second PDU session.

All the foregoing three solutions are applicable to a scenario in whichthe core network device has prepared a resource for establishing thefirst PDU session and the second PDU session. This scenario ishereinafter used as an example in this embodiment of this application.

In this embodiment of this application, the first access network devicemay send the first message to the core network device when determiningthat one or more of the following suspension conditions are met.Understandably, when the first message is used to indicate totemporarily reject the first PDU session and/or the second PDU session,the suspension condition may also be referred to as a temporaryrejection condition. A name is not limited in this application.

Suspension condition 1: The first access network device determines thatthere is no second access network device that can establish the secondPDU session. The second access network device and the first accessnetwork device are different access network devices. Unless otherwisespecified in this application, the second access network device is anaccess network device different from the first access network device.This also applies to the second access network device that appearshereinafter, and will not be reiterated.

The first access network device may determine, in the following manner,that there is no second access network device that can establish thesecond PDU session.

In a possible implementation, the first access network devicedetermines, based on a measurement report reported by the terminalinitiating establishment of the first PDU session and the second PDUsession, that there is no second access network device that can providea radio resource for the terminal, for example, no second access networkdevice whose channel status meets a communications requirement. In thisway, the first access network device may determine that there is nosecond access network device that can establish the second PDU sessionfor the terminal.

In another possible implementation, the first access network devicedetermines, based on the obtained load statuses of a plurality of accessnetwork devices, that there is no second access network device that canprovide radio resources for the terminal initiating establishment of thefirst PDU session and the second PDU session. For example, as learned bythe first access network device, the plurality of access network devicesare overloaded. In this way, the first access network device maydetermine that there is no second access network device that canestablish the second PDU session for the terminal.

Suspension condition 2: The first access network device determines thatthe terminal that initiates establishment of the first PDU session andthe second PDU session is unable to connect to the second access networkdevice. The terminal being unable to connect to the second accessnetwork device may also be understood as the terminal being unable toaccess the second access network device.

Suspension condition 3: The first access network device determinesinability to establish DC for the terminal that initiates establishmentof the first PDU session and the second PDU session. The inability ofthe first access network device to establish the DC for the terminal maybe understood as inability of the first access network device to add thesecond access network device to concurrently serve the terminal.

The first access network device may determine, in the following manner,the inability to establish the DC for the terminal.

In a possible implementation, the first access network device sends arequest for adding a second access network device, so that the secondaccess network device is requested to provide radio resources for theterminal initiating establishment of the first PDU session and thesecond PDU session. A radio resource management (RRM) entity of thesecond access network device rejects the request sent by the firstaccess network device and intended to add the second access networkdevice. Therefore, the first access network device determines inabilityto establish the DC for the terminal.

Suspension condition 4: The first access network device determines,based on a QoS parameter corresponding to a quality of service (QoS)flow of the first PDU session and/or the second PDU session, forexample, a reliability requirement, that the reliability requirement ismet by one PDU session (the first PDU session or the second PDU session)established on just one access network device (the first access networkdevice or the second access network device), without a need to establisha PDU session on the first access network device and the second accessnetwork device separately.

S102: After receiving the first message sent by the first access networkdevice, the core network device suspends one or both of the first PDUsession and the second PDU session based on the first message. This maybe understood as suspending the first PDU session and/or the second PDUsession.

Corresponding to the three solutions provided in step S101, thefollowing three solutions are provided in step S102:

First solution: The core network device suspends the first PDU sessionand the second PDU session based on the first message.

Second solution: The core network device suspends the first PDU sessionbased on the first message.

Third solution: The core network device suspends the second PDU sessionbased on the first message.

When the first solution is implemented in step S101, the correspondingfirst solution is also implemented in step S102. When the secondsolution is implemented in step S101, the corresponding second solutionis also implemented in step S102. When the third solution is implementedin step S101, the corresponding third solution is also implemented instep S102.

The following describes a meaning of suspending by using suspension ofthe first PDU session and the second PDU session as an example.Suspending the first PDU session and the second PDU session may mean norelease of a resource prepared for establishing/bearing the first PDUsession and the second PDU session.

S103: The first access network device sends activation information tothe core network device. The activation information is used to activatethe suspended first PDU session and/or second PDU session. The beingused to activate the suspended first PDU session and/or second PDUsession may also be understood as being used to resume the suspendedfirst PDU session and/or second PDU session. The activated/resumed firstPDU session and/or second PDU session may be understood as readiness forbeing used to transmit a data packet.

In a possible implementation, after receiving the activation informationsent by the first access network device, the core network device mayfurther send an acknowledgment message to the first access networkdevice, to acknowledge that the activation information is received.

The activation information may be carried in an existing message, forexample, may be carried in a PDU session resource modify indication (PDUsession resource modify indication) message, or may be carried in anewly added dedicated message, for example, may be carried in a newlyadded PDU session activation message or a PDU session resumptionmessage.

Optionally, the activation information may include a first identifierand/or a second identifier. For example, if the activation informationis used to activate the suspended first PDU session and second PDUsession, the activation information may include a first identifier and asecond identifier. For another example, if the activation information isused to activate the suspended first PDU session, the activationinformation may include the first identifier. For another example, ifthe activation information is used to activate the suspended second PDUsession, the activation information may include the second identifier.

Optionally, the activation information may further include an indicationinformation element. The indication information element may indicate toactivate the first PDU session and/or the second PDU session.

In this embodiment of this application, corresponding to the threesolutions provided in steps S101 and S102, the following three solutionsare provided in step S103.

First solution: The first access network device sends activationinformation to the core network device. The activation information isused to activate the suspended first PDU session and second PDU session.This solution is applicable to a scenario in which a reliabletransmission requirement between the terminal and the core networkdevice is not met by transmission of the data packet by using the firstPDU session alone or the second PDU session alone.

Second solution: The first access network device sends activationinformation to the core network device. The activation information isused to activate the suspended first PDU session. This solution isapplicable to a scenario in which the reliable transmission requirementbetween the terminal and the core network device is not met bytransmission of the data packet by using the second PDU session alone.

Third solution: The first access network device sends activationinformation to the core network device. The activation information isused to activate the suspended second PDU session. This solution isapplicable to a scenario in which the reliable transmission requirementbetween the terminal and the core network device is not met bytransmission of the data packet by using the first PDU session alone.

When the first solution is implemented in steps S101 and S102, thecorresponding first solution is implemented in step S103. When thesecond solution is implemented in steps S101 and S102, the correspondingsecond solution is implemented in step S103. When the third solution isimplemented in steps S101 and S102, the corresponding third solution isimplemented in step S103.

In an implementation, the first access network device establishes thefirst PDU session, and sends a first message to the core network device,where the first message is used to indicate to suspend the second PDUsession. In this case, the first access network device does notestablish the second PDU session.

In an implementation, the first access network device sends the firstmessage to the core network device, where the first message is used toindicate to suspend the first PDU session and the second PDU session. Inthis case, the first access network device may skip establishing thefirst PDU session and the second PDU session. Then, the first accessnetwork device may activate merely the first PDU session or the secondPDU session.

In this embodiment of this application, the first access network devicemay send the activation information to the core network device whendetermining that one or more of the following activation conditions aremet. The activation condition is also referred to as information aboutmeeting a condition for establishing the second PDU session, and thesecond access network device referred to hereinafter is a generic terminstead of a specific access network device. An access network devicethat does not meet the activation condition may be the same as ordifferent from an access network device that meets the activationcondition. For example, when the first access network device receivesthe second message, there is no access network device that meets thecondition for establishing the second PDU session. However, as load orchannel quality of the access network device changes, when an accessnetwork device that meets the condition for establishing the second PDUsession appears, the first access network device may send the activationinformation to the core network device.

Activation condition 1: The first access network device determines thatthere is a second access network device that can establish the secondPDU session.

The first access network device may determine, in the following manner,that there is a second access network device that can establish thesecond PDU session.

In a possible implementation, the first access network devicedetermines, based on a measurement report reported by the terminalinitiating establishment of the first PDU session and the second PDUsession, that there is a second access network device that can provide aradio resource for the terminal, for example, a second access networkdevice whose channel status meets a communications requirement. In thisway, the first access network device may determine that there is asecond access network device that can establish the second PDU sessionfor the terminal.

In another possible implementation, the first access network devicedetermines, based on the obtained load statuses of a plurality of accessnetwork devices, that there is a second access network device that canprovide radio resources for the terminal initiating establishment of thefirst PDU session and the second PDU session. For example, as learned bythe first access network device, the plurality of access network devicesare light-loaded. In this way, the first access network device maydetermine that there is a second access network device that canestablish the second PDU session for the terminal.

Activation condition 2: The first access network device determines thatthe terminal that initiates establishment of the first PDU session andthe second PDU session is able to connect to the second access networkdevice.

Activation condition 3: The first access network device determinesability to establish DC for the terminal that initiates establishment ofthe first PDU session and the second PDU session. The ability of thefirst access network device to establish the DC for the terminal may beunderstood as ability of the first access network device to add thesecond access network device to concurrently serve the terminal.

The first access network device may determine, in the following manner,the ability to establish the DC for the terminal.

In a possible implementation, the first access network device sends arequest for adding a second access network device, so that the secondaccess network device is requested to provide radio resources for theterminal that initiates establishment of the first PDU session and thesecond PDU session. The first access network device receives anacknowledgment message sent by the second access network device. Theacknowledgment message is used to indicate that the second accessnetwork device is ready to provide the radio resources for the terminal.In this way, the first access network device may determine that the DCcan be established for the terminal.

Activation condition 4: Based on a QoS parameter corresponding to aquality of service (QoS) flow of the first PDU session and/or the secondPDU session, for example, a reliability requirement, the first accessnetwork device determines that the reliability requirement is not metuntil a PDU session is established on the first access network deviceand the second access network device separately (for example, until afirst PDU session is established on the first access network device anda second PDU session is established on the second access networkdevice).

With reference to the process shown in FIG. 5, the following describesin more detail the communication method provided in this embodiment ofthis application. As shown in FIG. 6A and FIG. 6B, the process of thecommunication method is described below.

For steps S201 to S203, refer to the descriptions of steps S101 to S103,and details are omitted here.

In a possible implementation, after receiving the activation informationsent by the first access network device, the core network device mayactivate the suspended first PDU session and/or second PDU session basedon the activation information. Refer to step S204 in FIG. 6B. Forexample, if the activation information is used to activate the suspendedfirst PDU session, the core network device may activate the suspendedfirst PDU session based on the activation information. For example, ifthe activation information is used to activate the suspended first PDUsession and second PDU session, the core network device may activate thesuspended first PDU session and second PDU session based on theactivation information.

In this embodiment of this application, after being activated, thesuspended first PDU session and/or second PDU session may be used totransmit a data packet.

In this embodiment of this application, before the PDU sessionsuspension process is performed, a PDU session establishment process maybe further performed. The following describes a PDU sessionestablishment process. Refer to steps S200 a to S200 f in FIG. 6A.

S200 a: The core network device receives a first session establishmentrequest message from a terminal. The first session establishment requestmessage includes a first identifier used to identify a first PDUsession, and the first session establishment request message is used torequest to establish the first PDU session.

The core network device may receive the first session establishmentrequest message from the terminal by using the first access networkdevice. The first session establishment request message may be anon-access stratum (NAS) message.

S200 b: The core network device determines, based on the first sessionestablishment request message sent by the terminal, to establish thefirst PDU session.

S200 c: The core network device may further receive a second identifierfrom the terminal.

The core network device may receive the second identifier from theterminal by using the first access network device.

In this application, the second identifier may be carried in differentmessages for sending. The following describes two implementations ofsending the second identifier by the terminal.

In a possible implementation, the second identifier is carried in thefirst session establishment request message for sending.

In another possible implementation, the second identifier is carried ina second session establishment request message for sending. The secondsession establishment request message is used to request to establish asecond PDU session.

Optionally, the first session establishment request message may furtherinclude an association indication. The association indication is used toindicate that the first PDU session is associated with the second PDUsession. The association between the first PDU session and the secondPDU session may mean that the first PDU session and the second PDUsession are used to transmit duplicated data packets. For ease ofdescription, a PDU session used to transmit a duplicated data packet ishereinafter referred to as a duplicated or redundant PDU session. If thesecond identifier is carried in the second session establishment requestmessage, the association indication may include a first associationidentifier. The first association identifier may indicate that the firstPDU session is the 1st PDU session in the duplicated PDU sessions. Ifthe second identifier is carried in the first session establishmentrequest message, the association indication may include a firstassociation identifier and a second association identifier. The firstassociation identifier may indicate that the first PDU session is the1st PDU session in the duplicated PDU sessions, and the secondassociation identifier may indicate that the second PDU session is the2nd PDU session in the duplicated PDU sessions, or indicate that the 2ndPDU session is established on the second access network device.

Optionally, the second session establishment request message may furtherinclude an association indication, the association indication mayinclude a second association identifier, and the second associationidentifier may indicate that the second PDU session is the 2nd PDUsession in the duplicated PDU sessions. When the second identifier iscarried in the first session establishment request message, step S200 aand step S200 c in FIG. 6A may be combined into one step.

S200 d: The core network device determines, based on the received secondidentifier, to establish the second PDU session.

S200 e: After determining to establish the first PDU session and thesecond PDU session, the core network device may send a second message tothe first access network device. The second message includes the firstidentifier and the second identifier. The second message is used torequest to establish the first PDU session and the second PDU session.

Optionally, the second message may further include an associationindication. The association indication is used to indicate that thefirst PDU session is associated with the second PDU session. Theassociation between the first PDU session and the second PDU session maymean that the first PDU session and the second PDU session are used totransmit duplicated data packets. The association indication may includea first association identifier and a second association identifier. Thefirst association identifier may indicate that the first PDU session isthe 1st PDU session in the duplicated PDU sessions, and the secondassociation identifier may indicate that the second PDU session is the2nd PDU session in the duplicated PDU sessions.

Understandably, if the first session establishment request message orthe second session establishment request message includes no associationindication, the core network device may determine, based on a pre-agreedrule, whether the first PDU session and the second PDU session areduplicated PDU sessions. Certainly, the core network device may alsodetermine, based on the pre-agreed rule, which one of the first PDUsession or the second PDU session is the 1st PDU session in theduplicated PDU sessions, and which one is the 2nd PDU session in theduplicated PDU sessions.

Optionally, the second message may further include a restrictiveindication. The restrictive indication is used to indicate a restrictiverelationship by which the first PDU session can be established on aspecified access network device and the second PDU session can beestablished on another specified access network device. The restrictiveindication may include a first restrictive identifier. The firstrestrictive identifier may indicate a restriction by which the first PDUsession can be established on the first access network device alone, orcan be established on the second access network device alone, or can beestablished on either the first access network device or the secondaccess network device. The restrictive indication may further include asecond restrictive identifier. The second restrictive identifier mayindicate a restriction by which the second PDU session can beestablished on the first access network device alone, or can beestablished on the second access network device alone, or can beestablished on either the first access network device or the secondaccess network device. Understandably, the restrictive relationship maybe represented by an association indication. In this case, therestrictive indication may be omitted. Instead, based on the associationindication, the restrictive relationship is implicitly determined sothat the first PDU session can be established on a specified accessnetwork device and that the second PDU session can be established onanother specified access network device. For example, if the associationindication includes a first association identifier and a secondassociation identifier, the first association identifier indicates thatthe first PDU session is the 1st PDU session in the duplicated PDUsessions, and the second association identifier indicates that thesecond PDU session is the 2nd PDU session in the duplicated PDUsessions, then the 1st PDU session in the duplicated PDU sessions mayrepresent a restriction by which this PDU session can be established onthe first access network device, and the 2nd PDU session in theduplicated PDU sessions may represent a restriction by which this PDUsession can be established on the second access network device.

In a possible implementation, the sending the first identifier and thesecond identifier to the first access network device separately by thecore network device may also be understood as initiating, by the corenetwork device, a first PDU session establishment process and a secondPDU session establishment process toward the first access network deviceseparately. In this implementation, the terminal may sequentially send afirst session establishment request message and a second sessionestablishment request message to the core network device, to separatelyrequest to establish the first PDU session and the second PDU session.After the core network device determines, based on the first sessionestablishment request message and the second session establishmentrequest message separately, to establish the first PDU session and thesecond PDU session, the core network device sequentially sends a thirdmessage and a fourth message to the first access network device. Thethird message may carry a first identifier, and the fourth message maycarry a second identifier. The third message is used to request toestablish the first PDU session, and the fourth message is used torequest to establish the second PDU session. Optionally, in thisimplementation, the third message may further carry a first indication(also referred to as a first association identifier), used to indicatethat the first PDU session identified by the first identifier is the 1stPDU session in the duplicated PDU sessions. The fourth message mayfurther carry a second indication (also referred to as a secondassociation identifier), used to indicate that the second PDU sessionidentified by the second identifier is the 2nd PDU session in theduplicated PDU sessions.

S200 f: The first access network device determines, based on the secondmessage, to establish the first PDU session on the first access networkdevice, and to establish the second PDU session on the second accessnetwork device. As understood in a different way, the first accessnetwork device and the second access network device establish anend-to-end duplicated or redundant PDU session.

In a possible implementation, after step S200 e is performed, the firstaccess network device determines, based on the second message, toestablish the first PDU session and the second PDU session on the firstaccess network device. Alternatively, after step S200 e is performed,the first access network device determines, based on the second message,to establish the first PDU session and the second PDU session on thesecond access network device. In this implementation, redundancytransmission for the first PDU session and the second PDU session may beprovided on the first access network device or the second access networkdevice by using CA duplication.

In another possible implementation, after step S200 e is performed, thefirst access network device determines, based on the second message, toestablish the first PDU session and the second PDU session on the firstaccess network device and the second access network device. In thisimplementation, the redundancy transmission may be provided for thefirst PDU session and the second PDU session by using DC duplication.

Using an example in which the second message carries an associationindication, the first access network device may determine the 1st PDUsession and the 2nd PDU session in the duplicated PDU sessions based onthe association indication. For example, it may be determined that thefirst PDU session is the 1st PDU session in the duplicated PDU sessionsand that the second PDU session is the 2nd PDU session in the duplicatedPDU sessions. Therefore, the 1st PDU session may be established on thefirst access network device, and the 2nd PDU session may be establishedon the second access network device.

In this embodiment of this application, the second message may be a PDUsession request (PDU session request) message, a PDU session resourceestablishment request (PDU session resource setup request) message, orthe like.

Refer to Table 1, which shows a possible composition structure of thesecond message. Table 1 uses an example in which the second identifieris carried in the second message. Table 1 shows merely a part ofinformation elements of the second message. The second message furtherincludes other information elements in addition to the informationelements shown in Table 1. Table 1 is merely used as an example of apossible second message but not a limitation.

TABLE 1 Information element (Information Element, IE)/ PresentationSemantic description group name (Group Name) (presence) (Semanticsdescription) >>PDU Session ID M >>duplicated PDU session ID identifies aduplicated PDU session

In Table 1, the PDU Session ID may be a first identifier, and theduplicated PDU session ID may be a second identifier. Using an examplein which the second message is a PDU session resource establishmentrequest message, the duplicated PDU session ID is newly added content.Optionally, an association indication may be further added to Table 1and used to indicate that the first PDU session is associated with thesecond PDU session. For example, the association indication is used toindicate that a PDU session corresponding to the PDU session ID and aPDU session corresponding to the duplicated PDU session ID are used totransmit duplicated data packets. Optionally, a restrictive indicationmay be newly added to Table 1, and used to indicate a restrictiverelationship by which the first PDU session can be established on aspecified access network device and the second PDU session can beestablished on another specified access network device. For example, therestrictive indication may be used to indicate a restriction by whichthe PDU session corresponding to the PDU Session ID can be establishedon the first access network device alone, or can be established on thesecond access network device alone, or can be established andtransmitted on either the first access network device or the secondaccess network device.

In this embodiment of this application, the indication information maybe implemented in different forms. For example, the indicationinformation is implemented in an explicit form or an implicit form, asdescribed below separately.

1. Explicit Implementation.

For example, if the first message explicitly indicates to suspend thefirst PDU session and/or the second PDU session, the first accessnetwork device may directly add the first information element to thefirst message, to indicate to suspend the first PDU session and/or thesecond PDU session.

In the first message, for example, the first information element mayoccupy one or more bits, and the first access network device uses theone or more bits to indicate whether to suspend the first PDU sessionand/or the second PDU session. Using an example in which the firstinformation element occupies one bit, a value “0” of the bit mayindicate that no suspending of the first PDU session and/or the secondPDU session, and a value “1” of the bit may indicate suspending of thefirst PDU session and/or the second PDU session. Alternatively, using anexample in which the first information element occupies one bit, a value“0” of the bit may indicate that suspending of the first PDU sessionand/or the second PDU session, and a value “1” of the bit may indicateno suspending of the first PDU session and/or the second PDU session.This application does not limit the specific indication manner. In anexplicit implementation, the first information element is directlycarried in the first message, so that the indication is clearer.

Refer to Table 2, which shows a possible composition structure of thefirst message according to an embodiment of this application. Using anexample in which the first message carries a PDU session identifier (PDUsession ID) and a first information element (suspend), the firstinformation element is used to indicate to suspend the PDU sessioncorresponding to the PDU session ID. The PDU session ID in Table 2 mayinclude a first identifier and/or a second identifier. If the firstmessage is a PDU session resource establishment response message, thefirst information element (suspend) in Table 2 is newly added content.

TABLE 2 Information element (Information Element, IE)/ PresentationSemantic description group name (Group Name) (presence) (Semanticsdescription) >>PDU Session ID M >>suspend (suspend) indicates a need tosuspend the PDU session corresponding to he PDU Session ID

Refer to Table 3, which shows a possible composition structure of thefirst message according to an embodiment of this application. Using anexample in which the first message carries a PDU session identifier (PDUsession ID) and a first information element (reject), the firstinformation element is used to indicate to temporarily reject the PDUsession corresponding to the PDU session ID. The PDU session ID in Table3 may include a first identifier and/or a second identifier. If thefirst message is a PDU session resource establishment response message,the first information element (reject) in Table 3 is newly addedcontent. A location of the first information element (reject) in the PDUsession resource establishment response message is not limited.

TABLE 3 Information element (Information Element, IE)/ PresentationSemantic description group name (Group Name) (presence) (Semanticsdescription) >>PDU Session ID M >>reject (reject) indicates a need totemporarily reject the PDU session corresponding to the PDU Session ID

For example, if a message that carries activation information explicitlyindicates to activate the suspended first PDU session and/or second PDUsession, the first access network device may directly add an indicationinformation element into the message that carries the activationinformation, so that the indication information element is used toindicate to activate the first PDU session and/or the second PDUsession.

For example, if a message that carries deactivation informationexplicitly indicates to deactivate the first PDU session and/or thesecond PDU session, the first access network device may directly add anindication information element into the message that carries thedeactivation information, so that the indication information element isused to indicate to deactivate the first PDU session and/or the secondPDU session.

2. Implicit Implementation.

For example, if the first message implicitly indicates to suspend thefirst PDU session and/or the second PDU session, the first message sentby the first access network device does not need to carry additionalindication information, but the first message itself may be used asindication information.

For example, a protocol or a network device (the first access networkdevice and the core network device) may pre-specify that, if the firstmessage carries an identifier of the first PDU session and/or the secondPDU session, then the first message is used to indicate to suspend thefirst PDU session and/or the second PDU session. By using implicitindication, the first access network device does not need to add contentsuch as additional indication information into the message, therebyhelping to save transmission resources.

For example, if a message carrying activation information implicitlyindicates to activate the suspended first PDU session and/or second PDUsession, the message carrying the activation information does not needto carry additional indication information, but the message itself maybe used as indication information.

For example, if a message carrying deactivation information implicitlyindicates to deactivate the first PDU session and/or second PDU session,the message carrying the deactivation information does not need to carryadditional indication information, but the message itself may be used asindication information.

In this embodiment of this application, the core network device mayfurther receive the deactivation information from the first accessnetwork device. Referring to step S205 in FIG. 6B, the deactivationinformation may be used to indicate to deactivate the first PDU sessionand/or the second PDU session. After receiving the deactivationinformation sent by the first access network device, the core networkdevice may deactivate the first PDU session and/or the second PDUsession based on the deactivation information. Refer to step S206 inFIG. 6B.

After the PDU session is deactivated, the PDU session is unavailable fortransmitting a data packet. This may be understood as suspending the PDUsession again.

In a possible implementation, after performing an activation process,the first access network device and the core network device may performa deactivation process, that is, steps S205 to S206 in FIG. 6B.

In another possible implementation, the first access network device andthe core network device may perform a deactivation process afterperforming a PDU session establishment process. For example, theterminal may be concurrently connected to two access network devices,and may separately establish PDU sessions by using the two accessnetwork devices.

In the foregoing two implementations, the first access network devicemay initiate a deactivation process when determining that one or more ofthe following deactivation conditions are met.

Deactivation condition 1: The first access network device determinesthat the terminal is disconnected from the second access network device.

Deactivation condition 2: The first access network device determinesthat channel quality of the second access network device is too poor tomaintain DC.

Deactivation condition 3: The first access network device determinesthat a reliability transmission requirement is met by transmission ofthe data packet by using the first access network device alone.

Optionally, the deactivation information may include a first identifierand/or a second identifier. For example, if the deactivation informationis used to deactivate the first PDU session and second PDU session, thedeactivation information may include the first identifier and the secondidentifier. For another example, if the deactivation information is usedto deactivate the suspended first PDU session, the deactivationinformation may include the first identifier. For still another example,if the deactivation information is used to deactivate the suspendedsecond PDU session, the deactivation information may include the secondidentifier.

Optionally, the deactivation information may further include anindication information element. The indication information element mayindicate to deactivate the first PDU session and/or the second PDUsession.

In a possible implementation, after receiving the deactivationinformation sent by the first access network device, the core networkdevice may further send an acknowledgment message to the first accessnetwork device, to acknowledge that the deactivation information isreceived.

The following describes, by using an example, a communication methodaccording to an embodiment of this application with reference to FIG.7A, FIG. 7B, FIG. 8A, and FIG. 8B.

Refer to FIG. 7A and FIG. 7B, which are implementation flowcharts ofanother communication method according to an embodiment of thisapplication. FIG. 7A and FIG. 7B illustrate an example in which aterminal is UE, a first access network device is a RAN 1, a secondaccess network device is a RAN 2, and a core network device is an SMF.Referring to FIG. 7A and FIG. 7B, the method includes the followingsteps.

S301: An SMF receives a first session establishment request message fromUE. The first session establishment request message includes a firstidentifier. The first session establishment request message is used torequest to establish a first PDU session.

The SMF may receive, by using a RAN 1 and an AMF, the first sessionestablishment request message sent by the UE. For example, afterreceiving the first session establishment request message sent by theUE, the RAN 1 forwards the first session establishment request messageto the AMF. The AMF forwards the first session establishment requestmessage to the SMF after processing the message (for example, addingsome identification information into the message).

S302: The SMF determines, based on the first session establishmentrequest message sent by the UE, to establish the first PDU session.

S303: The SMF receives a second session establishment request messagefrom the UE. The second session establishment request message includes asecond identifier. The second session establishment request message isused to request to establish a second PDU session.

Similarly, the SMF may also receive, by using the RAN 1 and the AMF, thesecond session establishment request message sent by the UE. For adetailed process, refer to step S301, details of which are omitted here.

S304: The SMF determines, based on the second session establishmentrequest message sent by the UE, to establish the second PDU session.

S305: After determining to establish the first PDU session and thesecond PDU session, the SMF may send a message M31 to the RAN 1. Themessage M31 includes a first identifier and a second identifier, and themessage M31 is used to request to establish the first PDU session andthe second PDU session. For content that may be carried in the messageM31 and a meaning of the message M31, refer to the description of thesecond message in FIG. 6A, details of which are omitted here.

The SMF may send the message M31 to the RAN 1 by using the AMF.

This example is described below assuming that the message M31 carries anassociation indication and the association indication includes a firstassociation identifier and a second association identifier.

S306: After receiving the message M31, the RAN 1 may determine, based onthe first association identifier carried in the message M31, that thefirst PDU session is the 1st PDU session in the duplicated PDU sessions,and may determine, based on the second association identifier, that thesecond PDU session is the 2nd PDU session in the duplicated PDUsessions, so as to determine to establish the first PDU session on theRAN 1 and establish the second PDU session on the RAN 2. In this case,if determining that one or more of the suspension conditions are met,the RAN 1 sends a message M32 to the SMF. This example is describedassuming that the message M32 is used to indicate to suspend the firstPDU session and the second PDU session.

The RAN 1 may alternatively determine to establish the second PDUsession on the RAN 1 and establish the first PDU session on the RAN 2.This is not limited in this application.

S307: After receiving the message M32 sent by the RAN 1, the SMFsuspends the first PDU session and the second PDU session based on themessage M32.

In this way, when the RAN 1 is not ready to establish the DC, or, asunderstood in a different way, when there is no RAN 2 that can establishthe second PDU session, the RAN 1 may initiate a session suspensionprocess, for example, steps S306 to S307 in FIG. 7B. In this way, afterreceiving the message M32 sent by the RAN 1, the SMF suspends the firstPDU session and the second PDU session. In other words, the SMFtemporarily does not release resources for establishing the first PDUsession and the second PDU session, and may indicate, when the RAN 1 issubsequently ready to establish the DC, the SMF to activate thesuspended PDU session. In this way, a PDU session does not need to bere-established, and signaling overheads for establishing the PDU sessionare saved.

In this example, after initiating the session suspension process, theRAN 1 may further initiate a session activation process toward the SMFif the RAN 1 determines that one or more of the activation conditionsare met. Refer to steps S308 to S309 in FIG. 7B.

S308: The RAN 1 sends activation information to the SMF. This example isdescribed assuming that the activation information is used to activatethe suspended first PDU session and second PDU session. The RAN 1 maysend the activation information to the SMF by using the AMF.

S309: The SMF may activate the suspended first PDU session and secondPDU session based on the activation information.

In this example, after initiating the session activation process, theRAN 1 may further initiate a session deactivation process toward the SMFif the RAN 1 determines that one or more of the deactivation conditionsare met. Refer to steps S310 to S311 in FIG. 7B.

S310: The SMF receives deactivation information from the RAN 1. Thisexample is described assuming that the deactivation information is usedto indicate to deactivate the first PDU session and the second PDUsession.

S311: After receiving the deactivation information sent by the RAN 1,the SMF may deactivate the first PDU session and the second PDU sessionbased on the deactivation information.

Refer to FIG. 8A and FIG. 8B, which are implementation flowcharts ofanother communication method according to an embodiment of thisapplication. FIG. 8A and FIG. 8B illustrate an example in which aterminal is UE, a first access network device is a RAN 1, a secondaccess network device is a RAN 2, and a core network device is an SMF.Referring to FIG. 8A and FIG. 8B, the method includes the followingsteps.

S401: An SMF receives a first session establishment request message fromUE by using a RAN 1. The first session establishment request messageincludes a first identifier, and the first session establishment requestmessage is used to request to establish a first PDU session.

S402: The SMF determines, based on the first session establishmentrequest message sent by the UE, to establish the first PDU session.

For steps S401 to S402 in this example, refer to steps S301 to S302 inthe example shown in FIG. 7A, details of which are omitted here.

S403: After determining to establish the first PDU session, the SMF maysend a message M41 to the RAN 1. The message M41 carries the firstidentifier. The message M41 is used to request to establish the firstPDU session.

Optionally, the message M41 may further carry a first indication, usedto indicate that the first PDU session identified by the firstidentifier is the 1st PDU session in duplicated PDU sessions.

S404: The RAN 1 completes establishment of the first PDU session basedon the message M41.

In this example, the first PDU session and the second PDU session areestablished separately. In this way, after the establishment of thefirst PDU session is completed, a data packet may be transmitted betweenthe UE and the SMF by using the first PDU session.

S405: The SMF receives a second session establishment request messagefrom the UE by using the RAN 1. The second session establishment requestmessage includes a second identifier. The second session establishmentrequest message is used to request to establish a second PDU session.

S406: The SMF determines, based on the second session establishmentrequest message sent by the UE, to establish the second PDU session.

For steps S405 to S406 in this example, refer to steps S303 to S304 inthe example shown in FIG. 7A, details of which are omitted here.

S407: After determining to establish the second PDU session, the SMF maysend a message M42 to the RAN 1. The message M42 carries the secondidentifier. The message M42 is used to request to establish the secondPDU session.

Optionally, the message M42 may further carry a second indication, usedto indicate that the second PDU session identified by the secondidentifier is the 2nd PDU session in the duplicated PDU sessions.

S408: The RAN 1 determines to establish the second PDU session on a RAN2. In this case, if determining that one or more of temporary rejectionconditions are met, the RAN 1 sends a message M43 to the SMF. Thisexample is described assuming that the message M43 is used to indicateto temporarily reject the second PDU session.

S409: After receiving the message M43 sent by the RAN 1, the SMFdetermines, based on the message M43, to suspend the second PDU session.

In this way, when the RAN 1 is not ready to establish the DC, that is,when there is no RAN 2 that can establish the second PDU session, theRAN 1 may temporarily reject establishment of the second PDU session. Inthis case, the first PDU session already established is not affected. Inother words, in this case, a data packet can still be transmittedbetween the UE, the RAN 1, and the SMF by using the first PDU session.After receiving the message M43 sent by the RAN 1, the SMF temporarilyskips releasing a resource for establishing the second PDU session, andmay indicate, when the RAN 1 is subsequently ready to establish the DC,the SMF to activate the suspended second PDU session. In this way, a PDUsession does not need to be re-established, and signaling overheads forestablishing the PDU session are saved.

S410: The RAN 1 sends activation information to the SMF. In thisexample, it is assumed that the second PDU session is temporarilyrejected, and therefore, the activation information is used to activatethe suspended second PDU session. The RAN 1 may send the activationinformation to the SMF by using the AMF.

S411: The SMF may activate the suspended second PDU session based on theactivation information.

In this example, after initiating the session activation process, theRAN 1 may further initiate a session deactivation process toward the SMFif the RAN 1 determines that one or more of the deactivation conditionsare met.

For example, it is assumed that, after the activated second PDU sessiontransmits data packets for a period, channel quality of the RAN 2 usedto establish the second PDU session becomes so poor that the UE isdisconnected from the RAN 2. In this case, the RAN 1 may initiate adeactivation process for the second PDU session. Refer to steps S412 toS413 in FIG. 8B.

S412: The SMF receives deactivation information from the RAN 1. Thisexample is described assuming that the deactivation information is usedto indicate to deactivate the second PDU session.

S413: After receiving the deactivation information sent by the RAN 1,the SMF may deactivate the second PDU session based on the deactivationinformation.

The foregoing primarily describes the solutions provided in theembodiments of this application from a perspective of interactionbetween the first access network device and the core network device.Understandably, to implement the foregoing functions, the first accessnetwork device and the core network device include hardware structuresand/or software modules for performing the corresponding functions. Withreference to the units and algorithm steps described in the embodimentsdisclosed in this application, embodiments of this application can beimplemented in a form of hardware or hardware and computer software.Whether a function is performed by hardware or hardware driven bycomputer software depends on particular applications and designconstraints of the technical solutions. A person skilled in the art mayuse different methods to implement the described functions for eachparticular application, but it should not be considered that theimplementation falls beyond the scope of the technical solutions in theembodiments of this application.

In this embodiment of this application, functional units of the firstaccess network device and the core network device may be divided basedon the foregoing method examples. For example, the functional units maybe divided in such a way that each functional unit corresponds to aspecific function, or two or more functions may be integrated into oneprocessing unit. The integrated unit may be implemented in a form ofhardware, or may be implemented in a form of a software functional unit.

Based on a same inventive concept, the embodiments of this applicationfurther provide an apparatus configured to implement any one of theforegoing methods. For example, an apparatus is provided, and includesunits (or means) configured to implement the steps performed by thefirst access network device in any one of the foregoing methods. Foranother example, another apparatus is further provided, and includesunits (or means) configured to implement the steps performed by the corenetwork device in any one of the foregoing methods.

In a possible implementation, an embodiment of this application providesa communications apparatus 900. The communications apparatus 900 may beused in a first access network device. FIG. 9 is a schematic structuraldiagram of the communications apparatus 900 according to the embodimentof this application. Referring to FIG. 9, the communications apparatus900 may include a sending unit 901. In an implementation, thecommunications apparatus 900 may further include a receiving unit 902and a processing unit 903.

According to the communication method shown in FIG. 5, the sending unit901 in the communications apparatus 900 shown in FIG. 9 may beconfigured for the communications apparatus 900 to perform the stepshown in S101 or S103.

In another possible implementation, an embodiment of this applicationprovides a communications apparatus 1000. The communications apparatus1000 may be used in a core network device. FIG. 10 is a schematicstructural diagram of the communications apparatus 1000 according to theembodiment of this application. Referring to FIG. 10, the communicationsapparatus 1000 may include a receiving unit 1001 and a processing unit1002. In an implementation, the communications apparatus 1000 mayfurther include a sending unit 1003.

According to the communication method shown in FIG. 5, the receivingunit 1001 in the communications apparatus 1000 shown in FIG. 10 may beconfigured for the communications apparatus 1000 to perform the stepshown in S101 or S103, and the processing unit 1002 in thecommunications apparatus 1000 may be configured for the communicationsapparatus 1000 to perform the step shown in S102.

When the communications apparatus 900 is used in the first accessnetwork device, and the communications apparatus 1000 is used in thecore network device, the following operations may be further performed.

In a possible design, the receiving unit 902 is configured to: beforethe sending unit 901 sends a first message to the core network device,receive a second message from the core network device. The secondmessage includes a first identifier used to identify a first PDU sessionand a second identifier used to identify a second PDU session, and thesecond message is used to request to establish the first PDU session andthe second PDU session. According to this method, a PDU session does notneed to be re-established, and signaling overheads for establishing thePDU session are saved.

In another possible design, after the receiving unit 1001 receivesactivation information from the first access network device, theprocessing unit 1002 is further configured to activate a suspended PDUsession based on the activation information.

In still another possible design, the receiving unit 1001 is furtherconfigured to:

before receiving the first message from the first access network device,receive a first session establishment request message from a terminal,where the first session establishment request message includes the firstidentifier used to identify the first PDU session, and the first sessionestablishment request message is used to request to establish the firstPDU session.

The processing unit 1002 is further configured to determine, based onthe first session establishment request message, to establish the firstPDU session.

The receiving unit 1001 is further configured to receive, from theterminal, the second identifier used to identify the second PDU session.

The processing unit 1002 is further configured to determine, based onthe second identifier, to establish the second PDU session.

The sending unit 1003 is configured to send the second message to thefirst access network device. The second message includes the firstidentifier and the second identifier, and the second message is used torequest to establish the first PDU session and the second PDU session.

A message carrying the second identifier and sent to the communicationsapparatus 1000 is not limited in this embodiment of this application. Ina possible design, the first session establishment request messagefurther includes the second identifier. In another possible design, thesecond identifier is carried in a second session establishment requestmessage, and the second session establishment request message is used torequest to establish the second PDU session.

In still another possible design, the second message further includes anassociation indication. The association indication is used to indicatethat the first PDU session is associated with the second PDU session.

In still another possible design, the processing unit 903 is configuredto: determine, based on the second message, to establish the first PDUsession on the apparatus, and establish the second PDU session on asecond access network device.

That the sending unit 901 sends a first message to the core networkdevice specifically includes:

when the processing unit 903 determines that there is no second accessnetwork device that can establish the second PDU session, sending thefirst message to the core network device.

In still another possible design, that the sending unit 901 sends theactivation information to the core network device specifically includes:

when the processing unit 903 determines that there is a second accessnetwork device that can establish the second PDU session, sending theactivation information to the core network device.

In still another possible design, the sending unit 901 is furtherconfigured to:

send deactivation information to the core network device, where thedeactivation information is used to indicate to deactivate the first PDUsession and/or the second PDU session.

In still another possible design, after the receiving unit 1001 receivesthe deactivation information from the first access network device, theprocessing unit 1002 is further configured to deactivate the first PDUsession and/or the second PDU session based on the deactivationinformation.

In still another possible design, the deactivation information includesthe first identifier and/or the second identifier.

In still another possible design, the deactivation information includesan indication information element. The indication information element isused to indicate to deactivate the first PDU session and/or the secondPDU session.

In still another possible design, the first message includes a firstinformation element and/or a second information element. The firstinformation element is used to indicate to suspend the first PDU sessionand/or the second PDU session. The second information element is used toindicate a suspension cause.

In still another possible design, the activation information includesthe first identifier and/or the second identifier.

In still another possible design, the activation information includes anindication information element. The indication information element isused to indicate to activate the first PDU session and/or the second PDUsession.

It should be understood that division into the units in the foregoingapparatuses is merely logical function division. In an actualimplementation, all or some of the units may be integrated into aphysical entity, or may be physically separate. In addition, all theunits in the apparatuses may be implemented in a form of softwareinvoked by a processing element, or all may be implemented in a form ofhardware; or some units may be implemented in a form of software invokedby a processing element, and some units may be implemented in a form ofhardware. For example, each unit may be an independently disposedprocessing element, or may be integrated into a chip of the apparatusesfor implementation. Alternatively, each unit may be stored in a memoryin a form of a program to be invoked by a processing element of theapparatuses to perform a function of the unit. In addition, all or someof the units may be integrated together, or may be implementedindependently. The processing element herein may also be referred to asa processor, and may be an integrated circuit having a signal processingcapability. In an implementation process, the steps in the foregoingmethods or the foregoing units may be implemented by using a hardwareintegrated logic circuit of the processing element, or may beimplemented in a form of software invoked by the processing element.

In an example, a unit in any one of the foregoing apparatuses may be oneor more integrated circuits configured to implement the foregoingmethods, for example, one or more application-specific integratedcircuits (ASIC), one or more microprocessors (DSP), one or more fieldprogrammable gate arrays (FPGA), or a combination of at least two ofthese types of integrated circuits. For another example, when a unit inthe apparatuses is implemented in a form of a program invoked by aprocessing element, the processing element may be a general-purposeprocessor, for example, a central processing unit (CPU) or anotherprocessor that can invoke a program. For another example, the units maybe integrated together and implemented in a form of a system-on-a-chip(SOC).

The foregoing receiving unit is an interface circuit of the apparatus,and is configured to receive a signal from another apparatus. Forexample, when the apparatus is implemented in a form of a chip, thereceiving unit is an interface circuit that is of the chip and that isconfigured to receive a signal from another chip or apparatus. Theforegoing sending unit is an interface circuit of the apparatus, and isconfigured to send a signal to another apparatus. For example, when theapparatus is implemented in a form of a chip, the sending unit is aninterface circuit that is of the chip and that is configured to send asignal to another chip or apparatus.

FIG. 11 is a schematic structural diagram of a first access networkdevice according to an embodiment of this application. The first accessnetwork device is configured to implement operations of the first accessnetwork device in the foregoing embodiments. As shown in FIG. 11, thefirst access network device includes an antenna 1101, a radio frequencyapparatus 1102, and a baseband apparatus 1103. The antenna 1101 isconnected to the radio frequency apparatus 1102. In an uplink direction,the radio frequency apparatus 1102 receives, by using the antenna 1101,information sent by a terminal, and sends, to the baseband apparatus1103 for processing, the information sent by the terminal. In a downlinkdirection, the baseband apparatus 1103 processes the information fromthe terminal, and sends the information to the radio frequency apparatus1102. The radio frequency apparatus 1102 processes the information fromthe terminal, and then sends processed information to the terminal byusing the antenna 1101.

The baseband apparatus 1103 may include one or more processing elements11031, for example, include one main control CPU and another integratedcircuit. In addition, the baseband apparatus 1103 may further include astorage element 11032 and an interface circuit 11033. The storageelement 11032 is configured to store a program and data. The interfacecircuit 11033 is configured to exchange information with the radiofrequency apparatus 1102, and the interface circuit is, for example, acommon public radio interface (CPRI). The foregoing apparatus used inthe first access network device may be located in the baseband apparatus1103. For example, the foregoing apparatus used in the first accessnetwork device may be a chip on the baseband apparatus 1103. The chipincludes at least one processing element and an interface circuit. Theprocessing element is configured to perform the steps of any one of themethods performed by the first access network device. The interfacecircuit is configured to communicate with another apparatus. In animplementation, units of the first access network device that implementthe steps in the foregoing methods may be implemented in a form of aprogram invoked by a processing element. For example, the apparatus usedin the first access network device includes a processing element and astorage element. The processing element invokes a program stored in thestorage element, to perform the methods performed by the first accessnetwork device in the foregoing method embodiments. The storage elementmay be a storage element located on a same chip as the processingelement, that is, an on-chip storage element, or may be a storageelement located on a different chip from the processing element, thatis, an off-chip storage element.

In another implementation, units of the apparatus used in the firstaccess network device that implement the steps in the foregoing methodsmay be configured as one or more processing elements. These processingelements are disposed in the baseband apparatus. The processing elementherein may be an integrated circuit, for example, one or more ASICs, oneor more DSPs, one or more FPGAs, or a combination of these types ofintegrated circuits. These integrated circuits may be integratedtogether to form a chip.

Units of the first access network device that implement the steps in theforegoing methods may be integrated together, and implemented in a formof a system-on-a-chip (SOC). For example, the baseband apparatusincludes the SOC chip, configured to implement the foregoing methods. Atleast one processing element and a storage element may be integratedinto the chip, and the processing element invokes the program stored inthe storage element to implement the foregoing methods performed by thefirst access network device. Alternatively, at least one integratedcircuit may be integrated into the chip, to implement the foregoingmethods performed by the first access network device. Alternatively,with reference to the foregoing implementations, functions of some unitsmay be implemented in a form of a program invoked by the processingunit, and functions of some units may be implemented by using theintegrated circuit.

It can be learned that the foregoing apparatus used in the first accessnetwork device may include at least one processing element and aninterface circuit. The at least one processing element is configured toperform any one of the methods performed by the first access networkdevice provided in the foregoing method embodiments. The processingelement may perform, in a first manner, to be specific, by invoking theprogram stored in the storage element, some or all steps performed bythe first access network device; or may perform, in a second manner, tobe specific, by using a hardware integrated logic circuit in theprocessing element in combination with an instruction, some or all stepsperformed by the first access network device; or may certainly perform,by combining the first manner and the second manner, some or all stepsperformed by the first access network device.

As described above, the processing element herein may be ageneral-purpose processor, for example, a CPU, or may be one or moreintegrated circuits configured to implement the foregoing methods, forexample, one or more ASICs, one or more microprocessors DSPs, one ormore FPGAs, or a combination of at least two of the integrated circuits.

The storage element may be one memory, or may be a general term of aplurality of storage elements.

FIG. 12 is a schematic structural diagram of a core network deviceaccording to an embodiment of this application. The core network devicemay be the core network device in the foregoing embodiments and isconfigured to implement operations of the core network device in theforegoing embodiments.

As shown in FIG. 12, the core network device includes a processor 1210,a memory 1220, and an interface 1230. The processor 1210, the memory1220, and the interface 1230 are connected to each other by using asignal.

The communications apparatus 1000 is located in the core network device,and a function of each unit may be implemented by the processor 1210 byinvoking a program stored in the memory 1220. That is, the foregoingcommunications apparatus 1000 may include a memory and a processor. Thememory is configured to store a program, and the program is invoked bythe processor to perform the methods in the foregoing methodembodiments. The processor herein may be an integrated circuit having asignal processing capability, for example, a CPU. Alternatively,functions of the foregoing units may be implemented by one or moreintegrated circuits configured to implement the foregoing methods, forexample, one or more ASICs, one or more microprocessors DSPs, one ormore FPGAs, or a combination of at least two of the integrated circuits.Alternatively, the foregoing implementations may be combined.

According to the methods provided in the embodiments of thisapplication, an embodiment of this application further provides acommunications system. The system includes the foregoing first accessnetwork device, second access network device, core network device, andterminal.

An embodiment of this application further provides a communicationsapparatus, used in a first access network device or a core networkdevice, and including at least one processing element (or chip)configured to perform the foregoing method embodiments.

This application provides a communication program. When the program isexecuted by a processor, the processor is configured to perform themethods in the foregoing embodiments.

This application further provides a program product, for example, acomputer-readable storage medium, including the program in the foregoingcommunication methods.

A person skilled in the art should understand that the embodiments ofthis application may be provided as a method, a system, or a computerprogram product. Therefore, this application may use a form of hardwareonly embodiments, software only embodiments, or embodiments with acombination of software and hardware. Moreover, this application may usea form of a computer program product that is implemented on one or morecomputer-usable storage media (including but not limited to a diskmemory, a CD-ROM, an optical memory, and the like) that includecomputer-usable program code.

This application is described with reference to the flowcharts and/orblock diagrams of the method, the device (system), and the computerprogram product according to the embodiments of this application. Itshould be understood that computer program instructions may be used toimplement each process and/or each block in the flowcharts and/or theblock diagrams and a combination of a process and/or a block in theflowcharts and/or the block diagrams. These computer programinstructions may be provided for a general-purpose computer, a dedicatedcomputer, an embedded processor, or a processor of any otherprogrammable data processing device to generate a machine, so that theinstructions executed by a computer or a processor of any otherprogrammable data processing device generate an apparatus forimplementing a specific function in one or more processes in theflowcharts and/or in one or more blocks in the block diagrams.

These computer program instructions may be stored in a computer-readablememory that can instruct a computer or any other programmable dataprocessing device to work in a specific manner, so that the instructionsstored in the computer-readable memory generate an artifact thatincludes an instruction apparatus. The instruction apparatus implementsa specific function in one or more processes in the flowcharts and/or inone or more blocks in the block diagrams.

These computer program instructions may be loaded on a computer oranother programmable data processing device, so that a series ofoperation steps are performed on the computer or the anotherprogrammable device, thereby generating computer-implemented processing.Therefore, the instructions executed on the computer or the anotherprogrammable device provide steps for implementing a specific functionin one or more processes in the flowcharts and/or in one or more blocksin the block diagrams.

Although some possible embodiments of this application have beendescribed, a person skilled in the art can make changes andmodifications to these embodiments once learning the basic inventiveconcept. Therefore, the following claims are intended to be construed asto cover the embodiments of this application and all changes andmodifications falling within the scope of this application.

A person skilled in the art can make various modifications andvariations to this application without departing from the spirit andscope of this application. This application is intended to cover thesemodifications and variations of this application provided that they fallwithin the scope of protection defined by the following claims and theirequivalent technologies.

What is claimed is:
 1. A communication method, comprising: receiving, bya first access network device, a message from a core network device,wherein the message comprises an association indication, the associationindication indicates that a first protocol data unit (PDU) session isassociated with a second PDU session, the first PDU session and thesecond PDU session are used to transmit a duplicated data packet, andthe message comprises a first identifier used to identify the first PDUsession and a second identifier used to identify the second PDU session;and determining, by the first access network device based on themessage, to establish the first PDU session on the first access networkdevice, and to establish the second PDU session on a second accessnetwork device.
 2. The method according to claim 1, wherein theassociation indication comprises a first association identifier and asecond association identifier, the first association identifierindicates that the first PDU session is the a 1st PDU session induplicated PDU sessions, and the second association identifier indicatesthat the second PDU session is a 2nd PDU session in the duplicated PDUsessions.
 3. The method according to claim 1, wherein the message is aPDU session resource establishment request message.
 4. A communicationmethod, comprising: receiving, by a core network device, a first sessionestablishment request message and a second session establishment requestmessage from a terminal; determining, by the core network device basedon the first session establishment request message and the secondsession establishment request message, to establish a first protocoldata unit (PDU) session and a second PDU session, wherein the first PDUsession and the second PDU session are used to transmit a duplicateddata packet; sending, by the core network device, an associationindication to an access network device, wherein the associationindication indicates that the first PDU session is associated with thesecond PDU session; and sending, by the core network device, a firstidentifier used to identify the first PDU session and a secondidentifier used to identify the second PDU session to the access networkdevice.
 5. The method according to claim 4, wherein the associationindication comprises a first association identifier and a secondassociation identifier, the first association identifier indicates thatthe first PDU session is a 1st PDU session in duplicated PDU sessions,and the second association identifier indicates that the second PDUsession is a 2nd PDU session in the duplicated PDU sessions.
 6. Themethod according to claim 4, wherein the association indication iscarried in a PDU session resource establishment request message.
 7. Acommunications apparatus, comprising a processor and a memory storinginstructions that when executed by the processor configure thecommunications apparatus to: receive a message from a core networkdevice, wherein the message comprises an association indication, theassociation indication indicates that a first protocol data unit (PDU)session is associated with a second PDU session, the first PDU sessionand the second PDU session are used to transmit a duplicated datapacket, and the message comprises a first identifier used to identifythe first PDU session and a second identifier used to identify thesecond PDU session; and determine, based on the message, to establishthe first PDU session on the communications apparatus, and to establishthe second PDU session on a second access network device.
 8. Thecommunications apparatus according to claim 7, wherein the associationindication comprises a first association identifier and a secondassociation identifier, the first association identifier indicates thatthe first PDU session is a 1st PDU session in duplicated PDU sessions,and the second association identifier indicates that the second PDUsession is a 2nd PDU session in the duplicated PDU sessions.
 9. Thecommunications apparatus according to claim 7, wherein the message is aPDU session resource establishment request message.
 10. A communicationsapparatus, comprising a processor, wherein the processor and a memorystoring instructions that when executed by the processor configure thecommunications apparatus to: receive a first session establishmentrequest message and a second session establishment request message froma terminal; determine based on the first session establishment requestmessage and the second session establishment request message, toestablish a first protocol data unit (PDU) session and a second PDUsession, wherein the first PDU session and the second PDU session areused to transmit a duplicated data packet; send an associationindication to an access network device, wherein the associationindication indicates that the first PDU session is associated with thesecond PDU session; and send a first identifier used to identify thefirst PDU session and a second identifier used to identify the secondPDU session to the access network device.
 11. The communicationsapparatus according to claim 10, wherein the association indicationcomprises a first association identifier and a second associationidentifier, the first association identifier indicates that the firstPDU session is a 1st PDU session in duplicated PDU sessions, and thesecond association identifier indicates that the second PDU session is a2nd PDU session in the duplicated PDU sessions.
 12. The communicationsapparatus according to claim 10, wherein the association indication iscarried in a PDU session resource establishment request message.